Fuel cells can be a useful, efficient and environmentally friendly solution to power generation. They have few moving parts, and are highly efficient at converting energy contained in the fuel into usable electricity, and, in some cases, useable heat. Fuel cells generate direct current (D.C.). Generally, a fuel cell will generate D.C. at a voltage in the order of 1V, and, when operating under load, between 0.3V and 0.8V. The voltage changes, depending on the operating parameters of the fuel cells and the load drawn.
In general, the power from one fuel cell is insufficient to satisfy the electrical load requirements of the applications that fuel cells are provided for. Thus multiple fuel cells are connected together to form a fuel cell stack, with the preference to electrically connect the fuel cells in a series arrangement. A fuel cell stack includes additional items, including air and fuel manifolding and means of getting the electrical power out from the fuel cell stack.
A fuel cell system will incorporate at least one such fuel cell stack, as well as the fuel and air handling components (such as a blower, valves and filters), a control system, and the power electronics to allow the electrical power of the fuel cell to be converted to correct form to power the electrical load or loads to which it is connected. Such electrical loads could be direct current loads (DC loads) or alternating current loads (AC loads). Examples of such loads include batteries, pumps and blowers, motors, local mains, local grids and the national grid.
Fuel cells stacks can be used to provide electricity to an Alternating Current (A.C.) “grid” (such as the national grid in the UK). Alternative “grids” may include generators or stand-alone inverters connected to a D.C. source, in fact any A.C. system. Such fuel cell systems, when connected to the grid, provide a distributed network of power generation, and are particularly useful to provide extra power to a grid at times of peak power demand, when the grid is under heavy load. Due to their nature of operation, requiring fuel and air to be provided to the fuel cell under the right conditions of temperature, and in some cases pressure, fuel cell systems do not instantaneously start and stop generating electricity. Instead, they have “ramp up” and “ramp down” periods, between being completely off and at their operating capacity. Further, fuel cell systems require auxiliary devices, which enable the operation of the fuel cell stacks. Examples of such auxiliary devices are air blowers, which keep the operating temperature at the correct levels, and fuel pumps, which provide the fuel to the fuel cell stacks to enable them to generate power et cetera. Because the fuel cell stack generates D.C. voltage, and the grid requires A.C. voltage, conversion of the D.C. power is required by the fuel cell system when providing power to a grid. Because of the ramp time of a fuel cell stack, there are times when the auxiliary loads must be powered from the grid, so that they are always provided with operating power, even when the fuel cell stack is not providing power.